The present invention relates to a coordinates input apparatus. More particularly, the present invention relates to a coordinates input apparatus which detects elastic-wave vibration inputted to a vibration-transmitting tablet by vibration-input means, and obtains coordinates of the vibration-input point inputted by the vibration-input means based on the delay time of propagation of the elastic-wave vibration inputted to the vibration-transmitting tablet by the vibration-input means, and also relates to the vibration-transmitting tablet employed by the coordinates input apparatus.
A coordinates input apparatus employing an ultrasonic wave method calculates coordinates of a position by determining the delay time of a wave propagated on a tablet which serves as an input surface. According to the ultrasonic wave method, since no work has been done on the tablet such as matrix wiring or the like, it is possible to provide an inexpensive coordinates input apparatus. In addition, by using a transparent plate glass for a tablet, it is possible to provide a coordinates input apparatus having higher transparency as compared to apparatuses using other methods. In the coordinates input apparatus of this type, vibration applied to the vibration-transmitting tablet by a vibration-input pen is detected by a vibration sensor, and time difference between the vibration-applied time and vibration-detected time is calculated. By this, the distance from the vibration-applied point to the vibration sensor is calculated and a coordinates value of the vibration-applied point is obtained.
In a case where a glass plate is utilized as the vibration-transmitting tablet as mentioned above, the vibration-transmitting tablet can be broken by a strong impact load or extreme static pressure load. Therefore, in order to prevent injury of an operator, in case the glass plate is broken, one of the front surface (input side) or back surface of the vibration-transmitting tablet is laminated with resinous film. By virtue of the lamination, even in a case where the glass plate is broken, the operator does not have the risk of directly touching the broken glass plate, thus injury can be prevented. Moreover, the lamination has an effect of preventing scattering of broken pieces of glass. Film used for such lamination is not limited to a particular material; however, the film must adopt a material and thickness so that the film is not torn or split by pieces of broken glass plate.
As described above, the resinous film, used for laminating the glass plate for preventing scattering of broken pieces of glass in case the glass is broken, has a thickness such that the film is not torn or split by a piece of broken glass. Therefore, the film is uniaxially or biaxially stretched for improving mechanical strength. Because of the stretching processing, the film of this type has different mechanical characteristics depending on directions of the film. For instance, the elasticity (Young""s modulus), tensile strength, elongation and the like are different in the film rolled direction and the rolling axle direction orthogonal to the film rolled direction.
Vibration used in the coordinates input apparatus, employing an ultrasonic wave method, is a plate wave, and particularly, the vibration detected by the aforementioned vibration sensor is vibration in the Ao mode of the Lamb wave of a plate wave. The plate wave differs in its vibration propagation velocity (group velocity and phase velocity) depending upon the material characteristics (Young""s modulus, Poisson""s ratio and specific gravity) and thickness of the vibration-transmitting tablet, as well as the frequency of the vibration itself. In the case of the above-described vibration-transmitting tablet where a resinous film is laminated on the glass plate, vibration propagates on the plate which utilizes the combination of the glass plate having relatively fast propagation velocity and the resin having relatively slow propagation velocity. Therefore, the vibration propagation velocity on the vibration-transmitting tablet is slower than that on the glass plate. Furthermore, since the mechanical characteristics are different depending on which direction the film is stretched, a problem arises in that vibration propagation velocity differs depending on the directions. In other words, in a case where a film is laminated on a glass plate, the degree of slowing down the propagation velocity differs depending on directions of the film.
Moreover, for instance, in a case where vibration sensors are provided at positions 6a to 6d as shown in FIG. 1, the vibration sensors 6a and 6b detect vibration arriving from the vertical range of 180 degrees, and the vibration sensors 6c and 6d detect vibration arriving from the horizontal range of 180 degrees. Therefore, depending on a vibration-input point, the group velocity and phase velocity of the propagated plate wave become different values. As a result, a problem arises in that the actual vibration propagation velocity is different from a predetermined propagation velocity (group velocity and phase velocity) which has been set to calculate the distance. This causes an error when calculating the distance between the vibration-input pen and vibration sensor, consequently resulting in deterioration in precision of coordinates detection.
The present invention has been made in consideration of the above situation, and has as its object to provide a vibration-transmitting tablet, on which a protection film is laminated, which can minimize the changes in vibration propagation velocity in different directions of vibration propagation, and a coordinates input apparatus utilizing the vibration-transmitting tablet.
Another object of the present invention is to laminate a plurality of sheets of film on the vibration-transmitting tablet in such manner that the plurality of sheets of film can compensate influences over vibration propagation velocity, or such that influences over vibration propagation velocity are made equal in all directions, thereby satisfying the protection function and providing a vibration-transmitting tablet and coordinates input apparatus which can perform coordinates detection with high precision.
In order to attain the above objects, the vibration-transmitting tablet according to an embodiment of the present invention has the following configuration.
More specifically, the present invention provides a vibration-transmitting tablet for propagating inputted vibration, comprising: a substrate; and a plurality of films laminated on the substrate, wherein each of the plurality of films are laminated in an orientation such that the velocity of propagation of vibration in the axial direction are different from each other.
Furthermore, in order to attain the above objects, the coordinates input apparatus according to an embodiment of the present invention has the following configuration.
More specifically, the present invention provides a coordinates input apparatus for detecting vibration, inputted by vibration-input means, by a plurality of vibration sensors provided on a vibration-transmitting tablet, and deriving coordinates of a vibration-input point based on vibration transmitting time on the vibration-transmitting tablet, the vibration-transmitting tablet comprising: a substrate; and a plurality of films laminated on the substrate, wherein the plurality of films are laminated such that the velocity of propagation of vibration in the axial direction are different from each other.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.